§1.1 Field of the Invention
The present invention concerns methods, apparatus and data structures for providing a transport network that supports a virtual LAN service. More specifically, the present invention concerns emulating a transparent LAN segment to support a virtual LAN. The present invention also concerns configuring such a network.
§1.2 Related Art
The description of art in this section is not, and should not be interpreted to be, an admission that such art is prior art to the present invention.
§1.2.1 Known Private Networking Technologies
For many entities (such as businesses, universities, etc.), local area networks (or “LANs”) suffice for intra-entity communications. Indeed, LANs are quite popular since they are relatively inexpensive to deploy, operate, and manage, and are based on mature, well-developed technology, such as Ethernet, for example. Unfortunately, however, most entities need to communicate (voice and/or data) with their own facilities, or others, beyond their immediate location. Thus, wide area networks (or “WANs”) are needed. Very often, entities want at least some privacy or security attached to their communications.
Presently, private long-haul communications can take place over networks that can be generally classified into two types—dedicated WANs that facilitate communications among multiple sites, and public transport networks that allow one or more sites of a private network to communicate. Both of these types of networks are introduced below.
§1.2.1.1 Dedicated WANs
Dedicated wide area networks (“WANs”) are typically implemented using leased lines or dedicated circuits to connect multiple sites. Customer premise equipment (“CPE”) routers or switches at these sites connect these leased lines or dedicated circuits together to facilitate connectivity between each site of the network. Most private networks with a relatively large number of sites will not have “fully meshed” networks (i.e., direct connections between each of the sites) due to the cost of leased lines or dedicated circuits and to the complexity of configuring and managing customer premises equipment. Rather, some form of hierarchical network topology is typically employed in such instances. Dedicated WANs are relatively expensive and typically require the customer to have some networking expertise.
§1.2.1.2 Virtual Private Networks
Public transport networks, which are typically deployed by regional bell operating companies (or “RBOCs”), or some other service provider, are often used to allow remote users to connect to an enterprise network using the public-switched telephone network (or “PSTN”), an integrated services digital network (or “ISDN”), or some other type of transport network technology. (Note that the word “public” in the phrase “public transport network” connotes the fact that more than one entity may use it, even though it may be privately owned and managed, and not available to the general public.) Such remote access may be facilitated by deploying network access servers (or “NASs”) at one or more central cites. When users connect to (e.g., dial into) a NAS, it works with authentication, authorization and accounting (or “AAA”) servers to verify the identity of the user and to check which services that user is authorized to use.
§1.2.2 Limitations of Known Transport Network Technologies
As can be appreciated, private dedicated WANs are beyond the financial reach of many entities. Accordingly, so-called public transport networks have become quite popular. Unfortunately, however, various incompatible public transport networks have been introduced over the years in response to the then perceived needs to support various applications. Examples of such public transport network technologies include switched multimegabit data service (“SMDS”), X.25 packet switched networks, frame relay, broadband ISDN, and asynchronous transport mode (“ATM”).
The fact that public transport networks use incompatible technologies has two onerous implications for service providers. First, technologies with which customers access the transport network (referred to as “access technologies”) must be compatible with the technology used in the transport network (unless there is a handoff between networks, which is expensive). Thus, customers are locked into a technology from end-to-end. Further, such dependencies between access technologies and transport network technologies have forced public transport network service providers to support, maintain and administer separate networks.
Thus, an alternative public transport network is needed. Such a public transport network should (i) support the provision of virtual private network functions, (ii) isolate the transport network from incompetent or malicious actions by customers, (iii) be easy for a service provider to deploy (provision and configure) and manage, and/or (iv) allow customers to use a mature technology that is easy to install, use and manage, such as Ethernet for example, while shielding them from the complexities of the transport network.